The present invention relates to an improved clamping frame for supporting the peripheral edges of a sheet of thermoplastic material in a thermoforming apparatus.
Thermoforming apparatus for forming plastic sheets typically comprise a heating station and a molding station, and several carrier clamping frames are provided for gripping the edges of the plastic sheets so as to support the sheets at the heating station and moving them to the molding station. The clamping frames presently comprise a pair of pivotally connected gripping jaws and a pneumatic cylinder for opening and closing the jaws to grip the sheet. External hoses are provided for actuating each of the cylinders.
Thermoforming apparatus of the described type usually include a large number of such clamping frames, and the presence of the associated large number of hoses can interfere with the operation and movement of the clamping frames, and they are subject to leakage.
It is an object of the present invention to provide a clamping frame of the described type which has a reduced potential for air leaks, and thereby reduces maintenance. It is also an object to provide means for efficiently cooling the frame. Other objects include increasing the capacity and reliability of thermoforming machines of the described type.
The above and other objects and advantages of the invention are achieved by the provision of a clamping frame which comprises a pair of pivotally interconnected gripping jaws which are pivoted between open and closed positions by at least one actuator. The actuator comprises a fluid operated cylinder, and a fluid delivery system is provided for operating the actuator, which includes first and second fluid passages located within the jaw to which the actuator is attached.
In one preferred embodiment the actuator takes the form of an air cylinder which is mounted to one of the jaws and which includes a slideable piston. Fluid pressure ports are located at the opposite ends of the cylinder so that the piston can be biased and moved in either direction. The jaw to which the cylinder is mounted includes a mounting surface which includes outlets which communicate with respective ones of the fluid passages, and the cylinder is fixedly mounted to the jaw so as to overlie the mounting surface and so that the pressure ports communicate directly with respective ones of the outlets.
Thus with the present invention, leakage prone couplings between air hoses and the air cylinders are eliminated, and the problems of interference caused by the external hoses of the prior art are significantly alleviated. Also, the flow of the fluid (e.g. air) through the internal passages in the jaw tends to cool the jaws.